Automatic variable pitch pulley



Aug. 20, 1957 c. H. MINER AUTOMATIC VARIABLE PITCH PULLEY 2 Sheets-Sheetl Original Filed Dec.- 3. 1953 m .Y m M mh v m J mar/ 1% mar v wfw .Aug;20,1957 c, H, MlNER Re. 24,347

AUTOMATIC VARIABLE PITCH PULLEY Original Filed Dec. 3, 1953 2Sheets-Sheet 2 IN VEN TOR.

United States Patent ()filice Re. 24,347 Reissued Aug. 20, 1957 24,347AUTOMATIC VARIABLE PITCH PULLEY Charles Hugh Miner, Denver, Colo.,assigrior to Miner Pulley & Transmission Co., a corporation of ColoradoOriginal No. 2,711,103, dated June 21, 1955, Serial No. 395,912,December 3, 1953. Application for reissue June 28, 1956, Serial No.594,672

13 Claims. (Cl. 74-23017) Matter enclosed in heavy brackets I: 1 appearsin the original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to improvements in variable pitch V-type pulleysand has reference in greater particular to that type in which the pitchchanges automatically in response to belt tension or torque.

The present invention is an improvement or modification of the one shownand described in applicants copending application Serial No. 303,694,filed August 11, 1952, now Patent Number 2,699,071. Applicant admitsknowledge of the following U. S. patents: Hueber 1,279,547, September24, 1918 and Perrine 2,173,661, September 19, 1939.

Attempts have been made to develop variable pitch pulleys for use invariable speed belt transmissions as shown by the above identifiedpatents and by applicants prior Patent 2,553,505, May 15, 1951, all ofwhich, with the exception of Hueber, are provided with speed responsivecentrifugal means to effect the desired adjustment or which, likeHueber, depend for their functioning on the use of powerful helicalcompression springs which greatly shorten the lives of the belts and arethe cause of frequent belt failures.

It has been found that when pulleys ofthe type to which this inventionrelates are employed in a transmission that is used for a long time at afixed transmission ratio so that the side flanges of the pulley remainat a fixed distance from each other for long periods of time theydevelop a corrosion which is known by the name of fretting corrosion andwhich after some time locks the two parts so that they will not moverelative to each other and this makes them useless for speed regulation.It is one of the objects of this invention to produce a variable pitchpulley of this type that will not be subject to fretting corrosion andwhich therefore will always function properly.

It is a related object to achieve said result by employing a precessingbushing positioned between the contacting surfaces of the pulley parts,the bushing being free to rotate, for preventing the setting up offretting corrosion.

A further object is to produce a pulley of the type indicated that canoperate without a compression spring and which, when a spring is used,employs a weak spring that exerts a torsional force exclusively orcombined with a weak compression force.

This invention can be most clearly explained and will be most readilyunderstood by reference to the accompanying drawings in which theinvention has been illustrated, and in which,

Figure 1 is a longitudinal diametrical section through a pulleyconstructed in accordance with this invention, taken on line 1-1, Figure2;

' Figure 1a is a fragmentary detail showing certain parts to an enlargedscale;

Figure 2 is a transverse section taken on line 22, Figure -l;

Figure 3 is a; fragmentary section, similar to that shown in Figure 1but to an enlarged scale;

Figure 4 is a detail view showing a small section of the outer surfaceof the inner hub and shows the helical grooves with which it isprovided;

Figure 5 is a section taken on line 55, Figure 4;

Figure 6 is a multiple view taken on plane 66, Figure 3, and shows threeoptional constructions;

Figure 7 is a view showing a belt power transmission in which the pulleythat forms the subject of this invention is driven from a motor that isso mounted that the speed of the driven shaft can be changed by movingthe motor to change distance between the drive and driven shafts, thepulley being shown partly in section and partly in elevation;

Figure 8 is an end elevational view looking towards the left in Figure7;

Figure 9 is a fragmentary detail showing a portion of the outer surfaceof the inner hub and the position of the pin that connects the inner andouter hub when the pulley is driven from a motor as in Figure 7;

Figure 10 shows a belt transmission in which the pulley is mounted onthe movable motor of Figure 7 and transmits power to a driven shaft;

Figure 11 is a view similar to Figure 9 and shows the interconnectingpin and the oppositely inclined groove from that shown in Figure 9[;and].

[Figure 12 is a force diagram which will be referred to as thedescription proceeds] Referring now to the drawing reference numeral 15(Figures 7 and 10) represents the driving shaft which in this example ispart of motor M, and 16 is the driven shaft. In Figure 7 the pulley isdriven by the motor M and in Figure 10 the pulley is secured to themotor shaft. In both instances the motor transmits power to the drivenshaft by means of a belt 17 and is mounted for movement towards and awayfrom the driven shaft, as indicated by arrows.

The construction of the pulley will now be described. Referring now moreparticularly to Figures land 2, it will be seen that the pulleycomprises an annular flange 18 having an elongated hub 19 extending fromone side; the hub side of the flange has an outwardly flaringfrustoconical surface 20. The hub has a key way 21 for nonrotatablysecuring it to a shaft. Mounted on the outer surface of hub 19 is aco-operating flange 22 which has an elongated tubular hub 23. Theopening in hub 23 is somewhat larger than the outside diameter of hub 19except at its outer end where it has a narrow zone 24 that has an easysliding fit with hub 19. Positioned in the space between hubs 19 and 23are two thin bushings 25 and 25a which are held in place between flangeor zone 24 and a snap ring 26, shown most clearly in Figure la. Thecombined lengths of bushings 25 and 25a is less than the distancebetween flange 24 and ring 26 so that they can be separated by a space27. Bushings 25, 25a have a workable fit inside hub 23 and outside hub19 and are preferably made from sintered bronze or brass and haveinterstices which are filled with oil, such bushings are sold under thetrade name of Olite and are self lubricating or of any other suitablematerial such as those hereinafter pointed out. .Hub 19 is provided onits outer surface with two helical grooves 27D and 27F which areinclined in opposite directions as shown most clearly in Figure 4. Thereason for having two grooves is that the same pulley can then readilybe adapted for use on a driving shaft or on a driven shaft and forrotation in either direction all'as will be hereinafter explained. Theouter surface of hub 23 has a section 23a of enlarged diameter as shownmost clearly in Figures 3 and 10. From Figure 3 it will be seen that thethicker portion of hub 23,

whichhas been designated by 23a, has a radial opening in which ispositioned a steel pin 28 that extends through the space 27 between thebushings into one of the helical grooves 27P or 27D depending on whetherthe pulley is the power pulley or the driven pulley. The only reason forhaving the bushings made in two sections is to permit pin 28 to belocated in the most favorable position. -If the pin were positionedadjacent the outer end of hub 23 and adjacent flange 24, bushing 25,25a, could then be made in one piece. In Figures 1, 2 and 7, the pulleyis used on the driven shaft and rotates in the direction indicated byarrows but in Figure the pulley is on the motor shaft and delivers powerto belt 17. A screw 29 is so positioned that its head projects over theopening in which pin 28 is positioned and prevents the pin from fallingout. The pulley, as described above, can be employed as a driving pulleyas shown in Figure 10 where shaft is the motor or driving shaft and 16is the driven or load shaft which offers some resistance to turning. Letus now assume that the motor shaft begins to turn in the directionindicated by the arrow. Since the parts are at rest, pin 28 occupies theposition with respect to groove 27P substantially as shown in Figure 11and there is practically no side pressure on the belt. When the motor isenergized, hub 19 starts to turn, hub 23 lags due to its inertia and dueto some friction exerted thereon by the belt. The relative movement ofpin 28 and groove 27P moves flange 22 towards flange 18 and thiscompresses the belt until the friction becomes suflicient to make thebelt move. If the load increases sufficiently to cause the belt to slidealong inclined surface 20, flange 22 and hub 23 will turn relative tohub 19 and this will move flange 22 nearer to flange 18 until suflicientfriction is produced to transmit the desired load. When the current iscut 0d the motor tends to come to a sudden stop but flange 22 and hub 23will continue to move relative to hub 19 due to their momentum and thismovement will separate the pulley flanges to a maximum distance. Theinertia of flange 22 and attached parts will always produce a relativerotary movement with hub 19 and the inclined surface of flange 18 willinvariably be brought into contact with the belt. Attention is called atthis point to the important fact that when this pulley is used on adrive shaft to transmit power it requires no strings or centrifugalmeans to move the belt driving flanges towards each other and that itwill automatically adjust the pressure on the belt to produce therequired friction to carry theload. By adjusting the distance betweenthe drive and driven shafts the speed ratio can be varied. We will nowdirect our attention to Figures 7, 8 and 9 in which the pulley isattached to the driven shaft. Pin '28'has now'been transferred to groove27D as shown in Figure 9. 'Let us now assume that the parts areat restinstead of in operation as shown in Figure 7; nin'28 will then occupy:the position in groove 27D which has been designated by 28X and thebelt will then normally be out of contact with the inclined sides of theflanges and the pulley would not always start turning. To assure thatthere will always be sufficient pressure exerted on the'belt to producea relative rotation of hubs 23 and 19, a light helical or spiral spring29 has been added'to the parts shown in Figure 10 and the purpose ofthis will now'be described. In Figure 3 of the Hueber patent aboveidentified, a heavy helical compression spring has been shown in asomewhat similar relation to applicants spring, but it exerts no rotaryforce on the pulley flange for reasons apparent, excepting the minuteforce due to the component that results from the inclination of thethreads.

Referring now .to'Figures l, 2, 7 and '8, it will be seen that spring 29encircles hub 23 and has one endanchored to the end of hub section 23aas shownat30 in Figures 1 and '7. The other end is anchored to ring 31as shown at 32. The outer end of hub 19 is provided with a plurality ofangularly spaced notches 33 and ring 31 has at least one set screw 34whose point projects into a notch and secures the ring againstlongitudinal and rotarymovement. Ring 31 is also provided with aplurality of angularly spaced holes 35 in which the end of spring 29 canbe anchored. The torque force exerted by the spring can be adjustedeither by turning ring 31 on hub 19 or by shifting the end of the springto a diflerent hole. It will be noted from Figure 2 that spring 29 is soattached between hubs 19 and 23 that it exerts a torque that tends toturn flange 22 in the direction of belt travel and in such a way thatpin 28 will move relative to groove 27D in such a direction that it willmove flange 22 towards flange 18 and this assures that the sides of thebelt will always have suflicient frictional contact with the drivingsurface of flange 18 to provide the initial relative rotation betweenhubs 19 and 23 to produce positive operation whenever the motor isstarted. When the motor and belt are stopped the momentum of flange 18with its attached parts and the machine connected with shaft 16 willproduce a slight sliding of inclined surface 20 and the side of the beltin contact therewith while flange 22 will be stopped at the same time asthe belt and the relative rotation between hubs 19 and Y23 thus producedwill cause pin 28 to move upwardly in slot 27D and cause separation offlanges 18 and 22. The function of spring 29 is merely to assure thatthe side of flange 22 will always be in frictional engagement with thebelt, the spring can therefore be comparatively weak. Spring 29 willnormally be under some compressive strain at least suflicient to slidehub 23 on hub 19 and the torque action is so adjusted that it willproduce suflicient torque to make hub 23 turn sufficiently to let pin 28follow slot 27D with enough to spare to urge the driving surface offlange 22 into engagement with the co-operating belt surface. Although ahelical spring has been shown and is the type best suited for thispurpose, any

equivalent shaped spring can be substituted such as a spiral.

Pin 28 is free to turn and acts as a roller when it slides along groove27 as shown in the illustration C of Figure 6. This arrangement issatisfactory where the small amounts of power are transmitted. Where thestrains are too great for the arrangement C, the groove is made widerand pin 28 is surrounded by a freely rotatable ring 28a. Where largeamounts of power are transmitted, pin 28 can be provided with anelongated cross head-like slide as shown in Figure 6A in the place ofring 28a as shown in Figure 6B.

Particular attention is called to the great simplicity of this pulley inits simplest form, that shown in Figure 10. It consists of three parts.

Attention is called in particular .to the oil impregnated or other typeof bushings 25 and 25a which serve to preserve the free relativemovement between hubs 19 and 23 by preventing the setting up of frettingcorrosion [which is popularly believed to be due to the continuousprecessional movement of low and high pressure points] between theopposed surfaces of these concentric hubs [like 19 and 23].

As hereinbefore described, when a variable pitch pulley operating in atransmission, for long periods remains at a fixed transmission ratio, acorrosion develops between proximate surfaces of mating pulley partswhich locks the parts together preventing further relative movement oradjustment.

Fretting corrosion may be defined as corrosion at the interface betweentwo contacting surfaces, accelerated by vibration between the twosufiicient to produce localized deformation.

A reference to Figure 1 willshow that when thebelt is under tension itexerts [a spreading action on the flanges which is proportional to thebelt tension and is] a force on the concentric hubs bearing theseflanges. This force produces low and high pressure points betweenopposed surfaces of the concentric hubs which are always must be takento keep them properly lubricated.

at the same point relative to a line joining the axis of the driving andthe driven shafts. Since the pulley turns while [the] these low and highpressure points [of greatest spreading action] remain[s] stationary, itfollows .[that this point has] there is a continuous precessionalmovement or constant change in pressure around the cir cumference.[action that covers the entire circumference each rotation of the pulleyand this] This constant change in pressure produces slight movementbetween the opposed surfaces of the concentric hubs, a vibration, whichresults in the corrosion above referred to, [which] finally [prevents]preventing the free adjustment [that is] essential to satisfactoryoperation of such pulleys.

When the two hubs are separated by a rotatable bushing[s] [like thoseshown and designated by reference numerals and 25a] the precession ofthe low and high pressure points above referred to produces a slow butconstant rotation of the bushing[s] in the space between the two hubs,and this prevents the formation of [frittering] fretting corrosion. Thebushing [s] maybe made from any suitable material such as fiber,plastic, bronze, steel, or any other equivalent material. Sintered oilimpregnated bushings are preferred but are not essential. If ordinarybronze or fiber bushings are used, care It is not the material of whichthe bushings are made that prevents the [frittering] fretting corrosionbut the constant turning of the bushing in the space between the hubs.Oil impregnated bushings are desirable for obvious reasons. The use of aspring 29 can also be dispensed with as shown in Figure 10.

As has been pointed out above, a torsion spring functioning as describedis highly desirable even when no bushings are employed and that thebushings perform their function whether or not a spring is used.

What is claimed as new is:

l. A variable pitch pulley comprising, a first pulley member having acircular disk provided on one side with an elongated cylindrical hubprojecting therefrom, the hub side of the disk having the surface thatextends outwardly from the hub, beveled to form an outwardly flaringfrusto-conical belt engaging zone, a second pulley member comprising acircular disk of substantially the same diameter as the first disk, anelongated cylindrical tubular hub projecting from one side thereof, theopening in the last named hub being larger than the outside diameter ofthe first hub, a cylindrical bushing positioned in the space between thetwo hubs, the radial thickness of said space being sized to receive thebushing with a sliding fit, stop means at each end of the second hub forholding the bushing in position, the side of the second disk oppositefrom the hub being beveled to form a frusto-conical belt engaging zonethat faces the first frusto-conical zone forming with it a beltreceiving V-groove, the outer sur face of the first hub having at leastone helical groove, the second hub having a radial opening, a pinpositioned in the opening with its end positioned in the groove, thebushing being free to rotate relative to both hubs permitting it to turnin response to the precessional force produced by the unbalancedspreading force exerted on the pulley flanges by the spreading actionexerted thereon by the belt as the pulley is rotated.

2. A variable pitch pulley in accordance with claim 1 in which thebushing is made from oil impregnated metal.

3. A variable pitch pulley in accordance with claim 1 in which the outersurface of the first mentioned hub is provided with two oppositelyinclined helical grooves.

4. A variable pitch pulley in accordance with claim 1 in which a torsionspring operatively interconnects the two pulley parts and subjects themto a torsional force in a direction that tends to move the pin towardsthe flanged end of the first pulley member.

5. A variable pitch pulley comprising, a first pulley member having acircular disk provided on one side with an elongated cylindrical hubprojecting therefrom, the

hub side of the disk having the surface that extends out wardly from thehub, beveled to form an outwardly flaring frusto-conical belt engagingzone, a second pulley member comprising a circular disk of substantiallythe same diameter as the first disk, an elongated cylindrical tubularhub projecting from one side thereof, the opening in the last named hubbeing larger than the outside diameter of the first hub, a two partcylindrical bushing positioned in the space between the two hubs, theradial thickness of said space being sized to receive the bushing with asliding fit, stop means at each end of the second hub for holding thebushing in position, the side of the second disk opposite from the hubbeing beveled to form a frusto-conical belt engaging zone that faces thefirst frusto-conical zone forming with it a belt receiving V- groove,the outer surface of the first hub having at least one helical groove,the second hub having a radial opening, a pin positioned in the openingwith its end positioned in the groove, the bushing parts being spaced topermit the pin to pass into the groove, the bushing being free to rotaterelative to both hubs permitting it to turn in response to theprecessional force produced by the un-' balanced spreading force exertedon the pulley flanges by the spreading action exerted thereon by thebelt as the pulley is rotated.

6. A variable pitch pulley in accordance with claim 5 in which a torsionspring having a plurality of turns, encircles the hub portions, one endof the spring being connected with the first hub and the other end withthe second pulley part.

7. A variable pulley in accordance with claim 6 in which means isprovided for adjusting the tension of the spring, said means comprisingan annular flange attached to the end of the first hub and provided withopenings for anchoring the end of the torsion spring in difierentangular positions relative to the first hub.

8. A variable pitch pulley comprising, a first pulley member having acircular disk provided on one side with an elongated cylindrical hub,the hub side of the disk having an outwardly flaring belt engagingsurface, a second pulley member comprising a circular disk ofsubstantially the same diameter as the first disk, a tubular cylindricalhub projecting from one side of said second disk, the second hub beingmounted on the first hub for relative axial movement, the surface of thesecond disk that faces the first disk being outwardly flaring,'theopening in the second hub being larger than the outside of the first hubforming a cylindrical space, a bushing positioned in said space andsized to have a sliding fit with both the outer surface of the first huband the inside surface of the second hub, stop means at each end of theopening in the second hub for limiting the axial movement of thebushing, the outer surface of the first hub having a groove extending inthe general direction of the hub, a pin carried by the second hub andprojecting into the groove forming means to limit relative rotarymovement of the hubs while permitting relative axial movement, anabutment ring at the outer end of the first hub, and means positioned inthe space between the said abutment and the second disk for exerting onthe latter a force urging it to move relative to the first disk.

9. A variable pitch pulley comprising, in combination, a first pulleymember having a circular disc provided on one side with a surface thatis bevelled to form an outwardly flaring frusto-conical belt engagingzone, a second pulley member comprising a circular disc of substantiallythe same diameter as the first disc and presenting a side surfacebevelled to form a frusto-conical belt engaging zone that faces thefirst said zone, forming with it a belt receiving V-groove, said secondpulley member being journalled on said first pulley member for relativeaxial and angular movement, means for varying the axial spacing of thepulley members for varying the pitch of the pulley, and a precessingbushing positioned between the pulley members with a sliding fitrelative to each, the

bushing being .free .to rotate relative to both members, permitting.-it..to turn in response to precessional force produced :by thepressure exerted on the pulley members due to belt .tensionas thepulleyis rotated, whereby to prevent the setting up of fretting corrosionbetween the contacting surfaces of the pulley members.

10. A variable pitch pulley comprising, in combination, a first pulleymember. having a circular disc provided on one side with an elongatedcylindrical hub, the hub side of the disc having an outwardly flaringbelt engaging surface, a second pulley member comprising a circular discof substantially the same diameter as the first disc, said second pulleymember being journalled on the cylindrical hub presented by the firstpulley member for limited relative axial and rotational movement,said'hub extending inside the second pulley member, the surface of .thesecond disc that :faces the first disc being outwardly flaring andforming'with it a belt receiving V groove, and a-precessing bushingpositioned about said cylindrical hub "and inside the second pulleymember, the bushing being free to rotate relative to both'said hub andsaid second member, permitting the bushing to turn in response toprecessional force produced by the pressure exerted'on the'pulleymembers due to belt tension as the pulley is rotated, whereby to preventthesetting up of "fretting corrosion between the surface of. the hub onthe first pulley member and the concentric surface presented by theinside of the second pulley member.

1]. A variable pitch pulley comprising, in combination, a first pulleymember having a circular disc provided on one side with an elongatedcylindrical hub, the hub side of the disc having an outwardly flaringbelt engaging surface, a second pulley member comprising a circular discof substantially the same diameter as the first disc, said second pulleymember being journalled on the cylindrical hub presented by the firstpulley member'for limited relative axial and rotational movement, saidhub extending inside the second pulley member, the surface of the seconddisc that faces the first disc being outwardly flaring and forming withit a belt receiving V -gro'ove, spring means resiliently urging thepulley members towards each other, and a precessing bushing positionedabout said cylindrical hub and inside the second pulley member, thebushing being free to rotate relative to both the hub and the secondmember, permitting the bushing to turn in response to precessional forceproduced by the pressure exerted on the pulley members due to belttension as the pulley is rotated, whereby to prevent the setting up offretting corrosion between the surface of:the hub on the first pulleymember and the concentric surface presented by the inside of the secondpulley member.

12. .A variable pitch pulley comprising, in combination, a firstpulleymember havinga circular disc bevelled to form .an outwardly flaringfrusto-conical belt engaging zone, a second pulley member comprising acircular disc of substantially the same diameter as the first disc,bevelled to form a frusto-conical belt engaging zone that faces thefirst :said zone .-and forming with it a belt receiving V- groove, oneof said pulley-members having a hub projecting therefrom, the other ofsaid pulley members being journalled on :said hub for relative axial andangular movement, means resiliently urging the pulley members towardseach other, and a precessing bushing positioned between'said hub and theconcentric surface of the other pulley 'member with a-sliding fitrelative to each, the bushing being free to rotate relative to both thehub and the said'other pulley member, permitting it to turn'in responseto precessional force produced by the pressure exerted on the pulleymembers due to belt tension as the pulley is rotated, whereby to preventthe setting up of fretting corrosion" between the surface of the hub onthe -first pulley member and the contacting surface presented by thesecond pulley member.

J 3 A variable pitch pulley comprising, in combination, a first pulleymember having 'a circular disc provided on one side with an elongatedcylindrical hub, the hub side of the disc being bevelled to form an:outwardly flaring frusto-conical belt engaging zone, a second pulleymember comprising acircuiar disc of substantially the same diameterasthe first disc, said'second pulley member having a cylindricalborecentrally thereof in'which said cylindrical hub isreceived, thesecond pulley member being journalled on the hub for relative axial andangular move ment, the second disc being beveled to form a frustoconicalbelt engaging zone that faces the first said zone forming with it a beltreceiving V-groove, the bore in the second pulley member being larger insize than the outside of the hub on the first pulley member and leavinga cylindrical space about'the hub, and a precessing bushing posi--tionedin said space and sized to have a sliding fit with both the huband inside the bore, the bushing being free to rotate relative to bothof said pulley members, permitting the bushing to turn in response toprecessional force produced by the pressure exerted on the pulleymembers dueto belt tension as thepulley is rotated, whereby to preventthe setting up of fretting corrosion between the concentric surfacespresented by the hub on the first and the bore in the second of thepulley members.

References Cited in the file of this patent or the original patentUNITED STATES .PATENTS 834,212 Lohr Oct. 23, 1906 1,279,547 Hueber Sept.24, 1918 1,562,644 Jones Nov. 24, 1925 2,045,030 Thompson June 23, 19262,054,564 Quiroz Sept. 15,1936 2,171,741 Cohn Sept. 5, 1939 2,298,535Kreg Oct. 13, 1942 2,475,800 Munroe .July 12, 1949 2,678,566 Oehrli May18, 1954 FOREIGN PATENTS 2,160 Great Britain of 1912 591,319 GreatBritain Aug. 14, 1947

